This invention relates to bases for electric lamps and, in particular, to an improved base having reduced cost in terms of the material and energy used in the manufacture of the base.
Lamp bases are presently manufactured as completely assembled components in which a shell and eyelet are held in a mold into which molten glass is fed to form the insulator therebetween. As known in the art, this method of manufacture has some problems associated with it, viz, cracked or broken insulators and weakened base shells due to the annealing by the glass.
Various alternatives have been proposed for making bases, including mechanically assembled bases. In U.S. Pat. No. 3,775,634, several of these alternatives are noted along with a description of a mechanically assembled base in which a flange and groove at the lower end of the base shell are used to lock the previously formed insulator into place.
As known in the art, one of the advantages of the mechanically assembled base is that thinner material can be used for the shell. While the percent difference is small, that difference multiplied by the number of bases produced represents a considerable savings in material in the course of a year. Actually, the savings are somewhat greater since every base that is made does not wind up in a finished lamp.
However, reducing the amount of material in a base shell may result in cracking or tearing of the shell material. As is known in the art, working a metal increases its strength at the expense of increased brittleness. Forming the basefrom a blank increases the hardness of the already thinned material. Thus, subsequent working, e.g., rolling or turning, may result in the tool penetrating the shell. In the referenced patent, for example, the groove holding the insulator in place must be carefully formed to avoid penetrating the shell wall.